Sliding member and manufacturing method of sliding member

Abstract

To improve wear resistance while maintaining or improving low friction characteristics in a sliding member composed of cast iron.SOLUTION: A sliding member includes a substrate 11 composed of cast iron. The substrate 11 comprises an iron matrix 13 and a graphite structure 15, a part of which is present outside a surface of the iron matrix 13. The iron matrix 13 has, at the surface thereof, a first region and a second region having higher hardness than the first region.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a slide member and a method for manufacturing the slide member. [Background technology]

[0002] Patent Document 1 discloses a method for manufacturing a cast iron member having a sliding surface, in which a cast iron molded product having a specific composition is introduced into a heat treatment furnace and heat treated. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-105435 Summary of the Invention [Problem to be solved by the invention]

[0004] Cast iron is used in a wide range of sliding components as a low-friction material. There is a demand for technology to improve the wear resistance of sliding components using cast iron while maintaining or improving their low friction characteristics.

[0005] The present disclosure has been made in consideration of the above-described conventional situation, and aims to solve the problem of improving the wear resistance of a sliding member using cast iron while maintaining or improving low friction characteristics. [Means for solving the problem]

[0006] A sliding member having a base material made of cast iron, the substrate includes an iron matrix and a graphite structure, a part of which is present outside the surface of the iron matrix, The iron matrix has, on the surface thereof, a first region and a second region having a harderness than the first region. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a plan view of a sliding member according to an embodiment. [Figure 2] FIG. 2 is an enlarged view showing an area R1 in FIG. [Figure 3] 10A to 10C are diagrams illustrating a method for manufacturing a sliding member. [Figure 4] 1 is a microscopic image of the laser irradiated area of ​​FCD450 in preliminary experiment 1. [Figure 5] 1 is a microscope image of the laser irradiated area of ​​FCD600 in preliminary experiment 1. [Figure 6] 1 is a microscopic image of the laser irradiation site of FC250 in preliminary experiment 1. [Figure 7] 10 is a graph showing the relationship between irradiation time and dynamic hardness in preliminary experiment 2. [Figure 8] 1 shows microscopic images and cross-sectional curves of the surface of a test piece before and after roller burnishing. [Figure 9] 1 is a graph showing the change over time in the coefficient of friction of Example 1, Comparative Example 1, Comparative Example 2, and Reference Example. [Figure 10] 1 shows microscope images of the sliding surfaces of the test piece (disk) and the mating member (ring) after testing in Example 1, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] Also, preferred examples of the present disclosure will be described. [1] A sliding member having a base material made of cast iron, the substrate includes an iron matrix and a graphite structure, a part of which is present outside the surface of the iron matrix, The iron matrix has, on the surface thereof, a first region and a second region having a harderness than the first region. [2] The sliding member according to [1], wherein the second region is located at the center of a laser irradiated area formed by irradiating a laser. [3] The sliding member according to [1] or [2], wherein the second region has a Vickers hardness of 500 or more. [4] The sliding member according to any one of [1] to [3], wherein a graphite film derived from the graphite structure is formed. [5] A cast iron having a graphite structure protruding from the surface of the iron matrix is ​​prepared; a laser is irradiated onto the surface of the cast iron under conditions in which the protruding portions of the graphite structure do not disappear, thereby forming a region that is harder than a portion that is not irradiated with the laser. [6] The method for producing a slide member according to [5], wherein in preparing the cast iron, the surface of the cast iron is pressed to cause the graphite structure to protrude from the surface of the iron matrix. [7] The method for producing a sliding member according to [5] or [6], in which a graphite film derived from the graphite structure is formed.

[0009] The sliding member according to the embodiment will be described in detail below. In this specification, when a numerical range is indicated using "-", it is intended to include both the lower limit and the upper limit unless otherwise specified. For example, the expression "10-20" includes both the lower limit "10" and the upper limit "20". In other words, "10-20" has the same meaning as "10 or more and 20 or less".

[0010] As shown in Fig. 1 and Fig. 2, the sliding member 10 includes a base material 11 made of cast iron. A sliding surface 10A of the sliding member 10 is formed by the base material 11. In the sliding member 10 of Fig. 1, the area with a dot pattern is the sliding surface 10A that slides against the mating member 30. The shape of the sliding member 10 is not particularly limited. For example, the sliding surface may be a surface based on a flat surface, or may be the outer peripheral surface of a cylinder.

[0011] The type of cast iron is not particularly limited. The cast iron can be selected from the group consisting of, for example, spheroidal graphite cast iron, gray cast iron, white cast iron, mottled cast iron, blackheart malleable cast iron, whiteheart malleable cast iron, pearlitic cast iron, high-chromium cast iron, and high-silicate cast iron. When the cast iron is spheroidal graphite cast iron, the iron matrix 13 may be made of ferrite, since this allows the iron matrix 13 to contain a large amount of graphite structure 15. Examples of such cast irons include FCD370, FCD400, FCD450, and FCD500 (JIS standard). On the other hand, the iron matrix 13 may be made of pearlite. Examples of such cast irons include FCD600, FCD700, and FCD850 (JIS standard). Furthermore, the cast iron may be subjected to quenching, nitriding, or nitriding treatment.

[0012] Cast iron is widely used in machine structural parts due to its excellent vibration damping and friction and wear characteristics. The low wear characteristics of cast iron result from the graphite exposed on the surface forming a film that inhibits adhesion growth in the iron matrix. However, maintaining the graphite film involves wear of the iron matrix. On the other hand, improving wear resistance is effective in modifying the properties of the iron matrix so that the graphite film is effectively maintained while suppressing wear of the iron matrix. The present inventors conducted extensive research into maintaining the graphite film and improving wear resistance by hardening the surface, leading to the development of the technology disclosed herein.

[0013] The substrate 11 includes an iron matrix 13 and a graphite structure 15, a part of which is located outside the surface of the iron matrix 13, from the viewpoint of suppressing adhesion growth during sliding. In cast iron, the graphite structure 15 is, for example, spherical, flake, or other particulate. In this specification, the phrase "a part of the graphite structure 15 is located outside the surface of the iron matrix 13" may refer to a state in which a part of the graphite structure 15 protrudes from the surface of the iron matrix 13, as shown in FIG. 3(C). When an external force is applied to the graphite structure 15 in such a state due to sliding or the like, the protruding part of the graphite structure 15 is deformed or detached, and a graphite film 15A may be formed as shown in FIG. 3(E). The phrase "a part of the graphite structure 15 is located outside the surface of the iron matrix 13" may refer to a state in which a graphite film 15A derived from the graphite structure 15 is formed, as shown in FIG. 3(E). Specific examples of techniques for causing a part of the graphite structure 15 to "exist outside the surface of the iron matrix 13" will be described later.

[0014] The iron matrix 13 has a first region and a second region on its surface that is harder than the first region. Such first and second regions can be formed by irradiating the surface of the cast iron with a laser. For example, each of the partially missing circles in FIG. 2 represents a laser irradiated portion 20 formed by irradiating a laser. The laser irradiated portions 20 may be provided on the sliding surface 10A without any gaps, with adjacent laser irradiated portions 20 overlapping each other, as shown in FIG. 2. The laser irradiated portions 20 may also be provided with a gap between adjacent laser irradiated portions, with a portion not irradiated by the laser remaining between them.

[0015] The second region can be identified, for example, as the region of the sliding surface 10A that has the highest hardness. The second region is located, for example, at the center 20A of the laser-irradiated portion 20 formed by laser irradiation. A high-temperature field is formed in the center 20A of the laser-irradiated portion 20 by the laser irradiation. This induces a structural change in the iron matrix 13, hardening the iron matrix 13. Such heat treatment by laser irradiation allows for localized heating, a shorter heating time, and a faster cooling rate than heat treatments using other heat sources such as induction heating, an electric furnace, light heating, arc heating, and flame. Therefore, heat treatment by laser irradiation is considered to be particularly effective in surface modification of cast iron in that it can harden the iron matrix 13 while suppressing unnecessary diffusion of carbon into the iron matrix 13.

[0016] The first region can be identified, for example, as the region with the lowest hardness on the sliding surface 10A. When the laser irradiated portions 20 are overlapping and provided without gaps on the sliding surface 10A, the first region can be identified, for example, as the region of the periphery 20B of the laser irradiated portion 20. When the sliding surface has a portion that is not irradiated with laser (hereinafter also referred to as a non-laser irradiated portion 21), the first region can be identified, for example, as the region within the non-laser irradiated portion 21.

[0017] In other words, the surface of the iron matrix 13 may have a first region having a relatively low hardness and a second region having a relatively high hardness at the sliding surface 10A. Such a hardness difference is formed naturally by localized heating such as laser irradiation, and is one of the features that distinguishes it from a sliding surface obtained by uniformly heating the entire surface of cast iron.

[0018] Figure 7 shows the results of measuring the dynamic hardness of the laser-irradiated area of ​​each sample in Preliminary Experiment 2, which will be described later. The hardness of the center of the laser-irradiated area (circle plot) was greater than the hardness of the periphery of the laser-irradiated area (diamond plot). The hardness of the periphery of the laser-irradiated area (diamond plot) was greater than the hardness of the outside of the laser-irradiated area (triangle plot), i.e., the non-laser-irradiated area. This result also suggests that the center 20A of the laser-irradiated area 20 is harder than the non-laser-irradiated area 21 or the periphery 20B of the laser-irradiated area 20.

[0019] The Vickers hardness of the second region is preferably 220 or more, more preferably 500 or more, and even more preferably 700 or more. The Vickers hardness of the second region is not particularly limited as long as it is lower than the Vickers hardness of the mating member 30. If the Vickers hardness of the second region is lower than the Vickers hardness of the mating member 30, the graphite coating 15A can be suitably formed without scraping the sliding surface of the mating member 30. The Vickers hardness of the second region can be controlled, for example, by adjusting the laser irradiation conditions.

[0020] The Vickers hardness of the first region may be, for example, not less than 150 and less than 500, not less than 180 and not more than 400, or not less than 200 and not more than 300. The Vickers hardness of the first region can be controlled, for example, by appropriately selecting the type of cast iron material.

[0021] Next, the use and applications of the sliding member 10 will be described. The sliding member 10 is suitable as a sliding member that slides under dry conditions. Specifically, the sliding member 10 has a sliding surface 10A that slides against the sliding surface of a counter member 30, and no lubricating oil or grease may be present between the sliding surface 10A and the sliding surface of the counter member 30. The sliding member 10 can use graphite derived from the graphite structure 15 as a solid lubricant, thereby reducing the coefficient of friction.

[0022] Next, a method for manufacturing the slide member 10 will be described with reference to Fig. 3. The method for manufacturing the slide member 10 includes, for example, preparing cast iron having protruding graphite structure 15 on the surface of the iron matrix 13 (hereinafter also referred to as "preparing the cast iron"), and irradiating the surface of the cast iron with a laser under conditions that do not cause the protruding portion of the graphite structure 15 to disappear, thereby forming a region that is harder than a portion that is not irradiated with the laser (hereinafter also referred to as "forming a high-hardness region"). Furthermore, the method for manufacturing the slide member 10 may include forming a graphite film 15A derived from the graphite structure 15 (hereinafter also referred to as "forming a graphite film").

[0023] In preparing cast iron, for example, the surface of the cast iron may be pressed to cause the graphite structure 15 to protrude from the surface of the iron matrix 13. In raw cast iron, the graphite structure 15 is embedded in the iron matrix 13, as shown in FIG. 3(A). When the surface of the cast iron is pressed, the graphite structure 15 protrudes by being squeezed out from the iron matrix 13 due to differences in Young's modulus, as shown in FIG. 3(B). The surface pressure applied when pressing the surface of the cast iron may be, for example, in the range of 0.1 GPa to 3.0 GPa. The pressing of the cast iron surface can be performed by, for example, roller burnishing or shot peening. Roller burnishing is a technique in which a roller is pressed against the surface of the cast iron and moved while rotating. Note that the method for causing the graphite structure 15 to protrude from the surface of the iron matrix 13 is not limited to mechanical techniques such as roller burnishing or shot peening, and may also be an electrochemical technique such as etching or electropolishing. However, the mechanical method is suitable for manufacturing the slide member 10 in that components of the electrolyte solution and the like do not remain on the slide surface 10A.

[0024] In preparing the cast iron, there is no particular limitation on the height to which the graphite structure 15 protrudes from the surface of the iron matrix 13. The height to which the graphite structure 15 protrudes can be, for example, 0.1 μm or more and 10 μm or less, or 0.3 μm or more and 8 μm or less, or 0.5 μm or more and 5 μm or less.

[0025] To form the high-hardness region, the surface of the cast iron is irradiated with a laser under conditions that prevent the protruding portion of the graphite structure 15 from disappearing. The arrow in FIG. 3(C) schematically represents the laser. Graphite is a material with high laser absorption. In the cast iron of this embodiment, the graphite structure 15 protrudes from the surface of the iron matrix, so the temperature of the laser-irradiated portion 20 can be increased more favorably than in a configuration in which the graphite structure 15 is buried. Furthermore, a region that is harder than a portion not irradiated with the laser can be favorably formed in the laser-irradiated portion 20, particularly in its center 20A. That is, the cast iron of this embodiment can harden the iron matrix 13 without using a laser-absorbing agent or the like, thereby contributing to improved wear resistance.

[0026] The "conditions under which the protruding portions of the graphite structure 15 do not disappear" refer to, for example, conditions under which the graphite structure 15 is observed when the laser irradiated portion 20 is observed under a microscope. The fact that the protruding portions of the graphite structure 15 do not disappear can be confirmed by the formation of a graphite film 15A, which will be described later, when a sliding test is performed under dry conditions.

[0027] In forming the high-hardness region, the laser irradiation conditions can be appropriately set within a range in which a region having a higher hardness than a portion not irradiated with the laser can be formed and the graphite structure 15 does not disappear. The laser may be a pulsed laser or a CW (continuous wave) laser. From the viewpoint of reducing thermal effects, the laser is preferably a pulsed laser, and more preferably a short-pulse laser with a pulse width of 100 milliseconds or less. The laser irradiation device is not particularly limited, and known laser irradiation devices such as a YAG laser, a CO2 laser, an excimer laser, a He-Ne laser, a free electron laser, a semiconductor laser, and a dye laser can be used. The laser irradiation may be performed in an air atmosphere or an inert atmosphere (e.g., an N2 atmosphere or an Ar atmosphere). When the laser irradiation is performed in an inert atmosphere, the disappearance of the graphite structure 15 can be suitably suppressed.

[0028] The output of the laser can be, for example, 0.1 kW or more and 10 kW or less. When the laser irradiation range is substantially circular, the diameter of the laser irradiation range can be set according to the size of the graphite structure 15, and may be larger than the maximum diameter of the graphite structure 15 in a plan view, for example. The upper limit of the diameter of the laser irradiation range is not particularly limited as long as the effects of the present disclosure are achieved. The laser irradiation time can be, for example, 1.0 ms (milliseconds) or more and less than 20.0 ms (milliseconds). From the viewpoint of suppressing the disappearance of the graphite structure 15, the laser irradiation time is preferably 15.0 ms (milliseconds) or less, and more preferably 12.0 ms (milliseconds) or less.

[0029] In forming the high-hardness region, it is preferable to irradiate the laser in a spot pattern from the viewpoint of improving the cooling rate. For example, even when adjacent laser-irradiated areas overlap as shown in Figure 2, it is preferable to form one laser-irradiated area 20, then form another laser-irradiated area (not shown) that does not overlap the laser-irradiated area, and then form the other laser-irradiated area 20. In this way, by not irradiating the overlapping laser-irradiated areas 20 consecutively, the cooling rate of each laser-irradiated area 20 can be improved.

[0030] The method for forming the graphite film 15A is not particularly limited. In the manufacturing method of the slide member 10 of this embodiment, as shown in FIG. 3(C), even after the formation of the high-hardness region, the graphite structure 15 remains protruding from the surface of the iron matrix 13. As shown in FIG. 3(D), the slide member 10 in this state is caused to slide against a member harder than the graphite structure 15, such as a mating member 30, to suitably form the graphite film 15A. In the present disclosure, the phrase "the graphite film 15A can be formed" means that, when the slide member 10 is visually observed, a substantially uniform black film is observed on the surface of the iron matrix 13, as in the test piece (disk) of Example 1 in FIG. 10. In contrast, when the slide member 10 is visually observed and a black mottled pattern is observed, as in the test piece (disk) of Comparative Example 2 in FIG. 10, it is not said that "the graphite film 15A can be formed."

[0031] The manufacturing method of the slide member 10 of this embodiment may include steps other than the above steps as long as the effects of the present disclosure are not impaired. For example, in preparing the cast iron, the surface of the iron matrix 13 may be polished before pressing the surface of the cast iron. For example, in forming the high-hardness region, if the iron matrix 13 is deformed, such as raised, by laser irradiation, the surface of the iron matrix 13 may be flattened. [Example]

[0032] The present disclosure will be specifically described below with reference to examples, although the present disclosure is not limited thereto.

[0033] 1. Preliminary Experiment 1 Preliminary experiment 1 was conducted to confirm the change in hardness of the iron matrix of cast iron due to laser irradiation. (1) Preparation of test specimens As cast iron samples, FCD450 (spheroidal graphite cast iron), FCD600 (spheroidal graphite cast iron), and FC250 (gray cast iron) were prepared.

[0034] The surface of each sample was irradiated with a laser. A YAG laser irradiation device (wavelength 1064 nm) was used for the laser irradiation. The laser irradiation conditions were set in air as shown in Tables 1-3: laser output 1.0 kW-3.0 kW, spot diameter 0.2 mm-2.0 mm, and irradiation time 1.0 ms-20 ms. Figures 4-6 show microscope images of the laser irradiated areas of FCD450, FCD600, and FC250. The laser output (kW), spot diameter (mm), and irradiation time (ms) are shown above the microscope images.

[0035] The Vickers hardness was measured at the laser irradiated area of ​​each sample. For some samples, the Vickers hardness was measured at two different colored areas of the laser irradiated area (e.g., a white area and a brown area). The areas where the Vickers hardness was measured are shown by boxes in the microscopic images of Figures 4 to 6. The measured Vickers hardness values ​​are listed in Tables 1 to 3.

[0036] (2) Results of Preliminary Experiment 1 The results in Tables 1 to 3 show that irradiating the surface of cast iron with a laser can harden the iron matrix. The laser irradiated areas changed color from white to brown. The white areas were harder than the brown areas. It is believed that the white areas were hotter than the brown areas. Furthermore, in some samples, dendrites were formed in the white areas of the laser irradiated areas. This is thought to be evidence of localized melting and rapid cooling of the surface of the iron matrix due to laser irradiation.

[0037] In the sample with FCD450 and laser irradiation conditions of 1.0 kW, 0.2 mm, and 20 ms, the white area irradiated by the laser had a high Vickers hardness of 1106, but when observed under a microscope, no graphite structure was confirmed. This suggests that there is a trade-off between hardening the iron matrix and suppressing the disappearance of the graphite structure.

[0038] [Table 1]

[0039] [Table 2]

[0040] [Table 3]

[0041] 2. Preliminary Experiment 2 Preliminary experiment 2 was conducted to confirm the change in hardness of the iron matrix of cast iron due to laser irradiation. (1) Preparation of test specimens As a cast iron sample, FCD450 (spheroidal graphite cast iron) was prepared.

[0042] The surface of each sample was irradiated with a laser. A YAG laser irradiation device (wavelength 1064 nm) was used for laser irradiation. The laser irradiation conditions were set to an air atmosphere, laser output 1.0 kW, spot diameter 2.0 mm, and irradiation times of 1 ms, 5 ms, 10 ms, 15 ms, and 20 ms.

[0043] Dynamic hardness was measured for the laser irradiated area of ​​each sample. The measurement areas were the center, periphery, and outside of the laser irradiated area (area not irradiated with laser). The results are shown in the graph in Figure 7. The horizontal axis of the graph represents the irradiation time (ms), and the vertical axis represents dynamic hardness. In the graph, each plot represents data for the following measurement areas. Circle plot: Center of irradiated surface Diamond plot: Boundary of irradiated surface Triangular plot: Outside of the laser irradiation area

[0044] (2) Results of Preliminary Experiment 2 In the laser-irradiated area, the hardness of the center and periphery increased with increasing irradiation time. The hardness of the center of the laser-irradiated area was greater than the hardness of the periphery of the laser-irradiated area. The hardness of the periphery of the laser-irradiated area was greater than the hardness of the outside of the laser-irradiated area, i.e., the area not irradiated with laser. The hardness of the outside of the laser-irradiated area hardly changed even with increasing irradiation time. These results suggest that the iron matrix can be hardened even under relatively mild laser irradiation conditions, such as irradiation times of 1 ms to 15 ms.

[0045] 3. Experiments on combined processing of roller burnishing and laser irradiation Based on the results of Preliminary Experiments 1 and 2, we hypothesized that laser irradiation could simultaneously harden the iron matrix and prevent the disappearance of graphite structure, and conducted the following experiment with the aim of promoting graphite film formation. Specifically, in order to promote graphite film formation, a treatment was carried out on the surface of the iron matrix to make the graphite structure protrude.

[0046] (1) Preparation of test specimens Example 1 (Laser irradiation time 10 ms after roller burnishing) FCD450 (spheroidal graphite cast iron) was used for the test piece in Example 1. The test piece was machined by turning into a disk shape with an outer diameter of 44 mm, an inner diameter of 22 mm, and a thickness of 8 mm, and one end face of the disk was polished to a surface roughness of Ra 0.1 μm.

[0047] The surface of the test piece was subjected to roller burnishing using an SKD11 roller (Vickers hardness 850, diameter 37 mm, tip curvature 4 mm). Figure 8 shows the microscopic images and cross-sectional curves of the surface of the test piece before and after roller burnishing. The microscopic image and cross-sectional curve on the left (Mirror surface) are before roller burnishing, and after polishing. The microscopic image and cross-sectional curve on the right (Roller burnished) are after roller burnishing. It was found that roller burnishing can effectively protrude the graphite structure on the surface of the iron matrix.

[0048] The roller burnished surface of the test piece of Example 1 was irradiated with a laser. A YAG laser irradiation device (wavelength 1064 nm) was used for the laser irradiation. The laser irradiation conditions were set to an air atmosphere, a laser output of 1.0 kW, a spot diameter of 2.0 mm, and an irradiation time of 10 ms.

[0049] Comparison Example 1 (roller burnishing only, laser irradiation 0 ms) As Comparative Example 1, a test piece was prepared in the same manner as in Example 1, except that laser irradiation was not performed. Comparison Example 2 (Laser irradiation for 20 ms after roller burnishing) As Comparative Example 2, a test piece was prepared in the same manner as in Example 1, except that the laser irradiation time was set to 20 ms. Reference example (Laser irradiation 10ms later, roller burnishing) As a reference example, a test piece was prepared in the same manner as in Example 1, except that roller burnishing was carried out after laser irradiation.

[0050] (2) Friction test A ring-on-disc test was carried out under dry conditions on the disk test pieces according to Example 1, Comparative Example 1, Comparative Example 2, and Reference Example. An SUJ2 ring (Vickers hardness 800) was used as the mating material. The test conditions were as follows: Test load: 50N Test speed: 0.5 m / s Test environment: Temperature 23°C, humidity 29%, ambient air

[0051] (3) Experimental results on combined processing of roller burnishing and laser irradiation The change in the friction coefficient over time for Example 1, Comparative Example 1, Comparative Example 2, and Reference Example is shown in Figure 9. The horizontal axis represents the sliding distance (m), and the vertical axis represents the friction coefficient. Furthermore, Figure 10 shows microscope images of the sliding surfaces of the test pieces (disks) and the sliding surfaces of the mating members (rings) after testing for Example 1, Comparative Example 1, and Comparative Example 2.

[0052] The friction coefficient of Comparative Example 1 (roller burnishing only, laser irradiation 0 ms) was very low and stable at about 0.03 from the beginning, but suddenly increased when the sliding distance reached about 350 m. A graphite film was formed on the sliding surface of Comparative Example 1. The friction coefficient of Example 1 (after roller burnishing, laser irradiation time 10 ms) was approximately 0.03 from the beginning. The specific wear rate was also 6.8 × 10 -6 mm 3 / Nm. A graphite film was formed on the sliding surface of Example 1. The friction coefficient of Comparative Example 2 (laser irradiation for 20 ms after roller burnishing) was larger than those of Comparative Example 1 and Example 1. No graphite film was formed on the sliding surface of Comparative Example 2. The sliding surface of the mating side (ring) of Comparative Example 2 was discolored to reddish brown. The specific wear rate was also 6.3 × 10 -4 mm 3 / Nm, which was larger than that of Example 1. It is suggested that in Comparative Example 2, the protruding parts of the graphite structure may have disappeared due to the laser irradiation. In the reference example (laser irradiation 10 ms later, roller burnishing), the initial friction coefficient was about 0.05, and after a sliding distance of 100 m, it fluctuated between 0.1 and 0.2.

[0053] In Example 1, the graphite structure was first protruded, and then the surface of the cast iron was irradiated with a laser under conditions that did not cause the protruding graphite structure to disappear. Example 1 is considered to satisfy the following requirements (a) to (c). (a) A sliding member having a base material made of cast iron. (b) The substrate includes an iron matrix and a graphite structure, a part of which is present outside the surface of the iron matrix. (c) The iron matrix has, on its surface, a first region and a second region having a higher hardness than the first region.

[0054] In contrast, Comparative Example 1 does not satisfy requirement (c) because laser irradiation was not performed, and Comparative Example 2 does not satisfy requirement (b) because the protruding portions of the graphite structure disappeared.

[0055] It was suggested from Example 1, Comparative Example 1, and Comparative Example 2 that the wear resistance can be improved by hardening the iron matrix by laser irradiation. Furthermore, it was suggested that by protruding graphite before laser irradiation and then irradiating the surface of the cast iron with a laser under conditions that do not cause the protruding graphite structure to disappear, it is possible to suppress the growth of adhesion with the mating material and reduce the coefficient of friction.

[0056] 4. Effects of the Example According to this example, in the sliding member using cast iron, it was possible to improve the low friction characteristics and the wear resistance.

[0057] The present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the claims of the present disclosure. [Explanation of symbols]

[0058] 10...sliding member, 10A...sliding surface, 11...substrate, 13...iron matrix, 15...graphite structure, 15A...graphite film, 20...laser irradiated area, 20A...center, 20B...periphery, 21...laser non-irradiated area, 30...counterpart

Claims

1. A sliding member having a base material made of cast iron, the substrate includes an iron matrix and a graphite structure, a part of which is present outside the surface of the iron matrix, The iron matrix has, on the surface thereof, a first region and a second region having a harderness than the first region.

2. The sliding member according to claim 1 , wherein the second region is located at the center of a laser irradiated portion formed by irradiating a laser.

3. 3. The sliding member according to claim 1, wherein the second region has a Vickers hardness of 500 or more.

4. 3. The sliding member according to claim 1, wherein a graphite film derived from the graphite structure is formed.

5. preparing a cast iron having a graphite structure protruding from the surface of an iron matrix; a laser is irradiated onto the surface of the cast iron under conditions in which the protruding portions of the graphite structure do not disappear, thereby forming a region that is harder than a portion that is not irradiated with the laser.

6. 6. The method for producing a slide member according to claim 5, wherein in preparing the cast iron, the surface of the cast iron is pressed to cause the graphite structure to protrude from the surface of the iron matrix.

7. The method for producing a slide member according to claim 5 or 6, wherein the graphite film derived from the graphite structure is formed.

Images